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40K Loremasters: The 20 Space Marine Legions

5 Minute Read
Mar 7 2019


Long before they were chapters – the Astartes conquered the galaxy in twenty great legions. Here is what is known of them Loremasters:

The twenty Space Marine Legions, also known as the Legiones Astartes, were created by the Emperor to take part in the Great Crusade in what was later known as the First Founding. All the Space Marines of a Legion (“battle-brothers” amongst themselves) were modified with help of the DNA samples of a single Primarch. As a Primarch was found, he would receive the command of his respective Legion.


The Legiones Astartes were originally created by the Emperor and his gene-wrights in the closing days of the Unification Wars and the extinction of their predecessors, the Thunder Warriors. The new Astartes had superior lifespans and discipline to the Thunder Warriors, and were intended by the Emperor to spearhead his coming Great Crusade. Each of the twenty Legions were created from gene-seed derived from a single Primarch, which were themselves maturing deep under the Himalayan Mountains before they were stolen away from the Forces of Chaos. However while the Gene-Seed was created by the Emperor, it was perfected and mass-produced by the Gene-Cults of Luna after they were pacified by the early Astartes.

During the subsequent Great Crusade, the twenty Legiones Astartes were the tip of the Emperor’s spear in his conquest of much of the galaxy. Gradually, the twenty lost Primarchs were reunified with their respective Legion and led them to further glories, where they would begin to establish unique identities for themselves. However some point during the Great Crusade, two of the legions were erased from all records for unknown reasons.

In the Horus Heresy, nine of the eighteen remaining Legions sided with Warmaster Horus against the Emperor. After the Battle of Terra, these fled into the Eye of Terror where many fragmented into disparate warbands that continue to plague the Imperium to this day. The remaining loyalist Legions were broken up by Roboute Guilliman as per the new Codex Astartes. The Space Marine Legions effectively ceased to exist after this act, succeeded by hundreds of new Chapters.


Legion Structure

The Legio Astartes, being far larger then current Space Marine Chapters, were organized along drastically different lines. At the head of the Legion was its Primarch Commander who oversaw the Legion’s headquarters. Below this were the Chapters of the Legion, each of which was commanded by a Chapter Commander. Each Chapter in turn was divided into a number of Battalions, each of which was further divided into Companies. The Company, itself divided into a number of Squads, was the basic military division of the Legio Astartes. Due to the varying sizes of each Legion, there was no fixed number of how many Chapters, Battalions, Companies, and Squads a Legion would contain.

Number of Legionaries

The Legions were massive armies, and the size of each could vary tremendously. A precise number was never truly achieved and maintained. Even during the Great Crusade, some Legions were very numerous, while others were not. The numbers would always vary with new recruits and inevitable battle-losses, and also important was the availability of potential recruits and the administrative skills of the Primarch and his officers.

The most numerous Legion of all was the Ultramarines. The Thousand Sons of Magnus were of a small number as many of them had developed mutations or uncontrollable levels of psychic powers. Fulgrim‘s samples had been largely lost, and this left the Legion of the Emperor’s Children also with a very small number. Both of these Legions would increase their numbers to acceptable standards only after their Primarchs were found.


The approximate sizes of a few of the Legions at the start of the Heresy have been given in various sources:


The Legion size issue is contentious, with several types of numbers mentioned in separate sources meant to reflect a general or nominally-sized legion. As well as numbers directly given in sources themselves, several authors have commented on the issue. Pressed with questions about pre-Heresy organisation – although declaring there is not any real information about it – Andy Chambers answered that “Space Marines started out in Legions of approximately 10,000 strong (or more, depending on the specific legion), which were broken down into Chapter-sized Great Companies rather like the Space Wolves (who are renowned for not adopting the Codex Astartes alterations made by Guilliman post-heresy and who thus follow pre-heresy organisation more closely”.

  • Note 1: In The Crimson Fist (Novella) it is mentioned that 20,000 Imperial Fists constituted one-fifth of the entire Legion, making 100,000 the likely number.
  • Note 2: In A Thousand Sons (Novel), during the Battle of Prospero it is mentioned that Ahriman counts about 1,000 survivors from the legion and states that it is “tenth of the Legion” which makes the Thousand Sons about 10,000 men before the Space Wolves attack Prospero.
  • Before the Word Bearers invasion to Boros Gate it is mentioned the Black Legion’s strength is unparalleled and that their rank their ranks outnumbered the Word Bearers by almost ten to one. If at that point the Word Bearers kept the ranks at the size of 100,000 space marines it means the Black Legion have vastly increased their numbers to around 1,000,000 space marines.
  • Note 3: Further down the page of the cited source, Betrayal states that this number is leading up to Istvaan III. After the conflict, some 60,000 Sons of Horus Astartes were lost, some of which are the Loyalists. After the betrayal at Istvaan III, the current numbers of the Sons of Horus are estimated to be 70,000-110,000.

Forge World Tactical Legion Marine

Original Names and Appearances

Originally, each Legion was known simply by its number (i.e., the Dark Angels were originally known as Ist Legion) and had plain grey armour. However upon rediscovering their Primarch the Legion would take his homeworld as their own, gain a name instead of just being known by their number, and change their Power Armour from grey to one consisting of a combination of battle honours and their Primarch’s own tastes.

The Emperor saw no problems with this development; the loyalty of the Primarchs to him was believed to be unshakable. This reasoning would be proven to be sadly mistaken as half of the known Legions revolted during the Horus Heresy.


The Twenty Space Marine Legions of the Great Crusade

Number Name Original name Primarch Homeworld Loyalty
I Dark Angels The First Lion El’Jonson Caliban Loyal
II Unknown – All records lost following the Horus Heresy.
III Emperor’s Children unknown Fulgrim Chemos Traitor
IV Iron Warriors —- Perturabo Olympia Traitor
V White Scars —- Jaghatai Khan Mundus Planus Loyal
VI Space Wolves —- Leman Russ Fenris Loyal
VII Imperial Fists —- Rogal Dorn Terra Loyal
VIII Night Lords —- Konrad Curze Nostramo Traitor
IX Blood Angels —- Sanguinius Baal Loyal
X Iron Hands Storm Walkers Ferrus Manus Medusa Loyal
XI Unknown – All records lost following the Horus Heresy.
XII World Eaters War Hounds Angron Bodt Traitor
XIII Ultramarines —- Roboute Guilliman Macragge Loyal
XIV Death Guard Dusk Raiders Mortarion Barbarus Traitor
XV Thousand Sons —- Magnus Prospero Traitor
XVI Sons of Horus Luna Wolves Horus Lupercal Cthonia Traitor
XVII Word Bearers Imperial Heralds Lorgar Aurelian Colchis Traitor
XVIII Salamanders Dragon Warriors Vulkan Nocturne Loyal
XIX Raven Guard —- Corvus Corax Deliverance Loyal
XX Alpha Legion —- Alpharius Unknown Traitor

Learn More of the Missing Legions



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